Official Luthiers Forum!

So we got a few glue threads going so why not have a spin-off. Anyone using HHG Rub Joints for anything? I read around on the World Wide Web some folks are claiming they are gluing top braces down with HHG rub joints no clamp & no go bars just rub and hold in place a minute or two any are claiming no issues! You guys buying this? If you had to put money down on a break test who’s coming out on top HHG rub joint or white glue clamp joint?

My bet would be that the wood would still fail before the glue in either case.

Yeah I’m betting the wood will fail as well unless the wood is large dimensionally in comparison to the joint. After thanksgiving I may have to do some testing so I can report back. I got some tight bond and some 192 hide.

I do rubbed HHG on my classical bracing. In destructive testing I can't tell the difference between the rubbed HHG and clamped TB. I vaccuum clamp classical bridges, though, to protect the top finish.

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formerly known around here as burbank
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http://www.patfosterguitars.com

I've done HHG rubbed joints to glue bridges on nylon stringed instruments that have relatively flat tops. They seem to hold up O.K.
With top braces I am usually pressing them into a solera to arch the top, so I use go bars. As I understand it the purpose of rubbing the joint is to thin out the glue line, and the joint pulls tighter as the glue dries.

Yeah I believe a fresh HHG joint is probably os going to do as well as anything else except when thing like X braces and such with the curve like you kind of referenced.

Curious how long to you hold them down before release? How does this work with the arching?

I would say rub joint, except the white glue would also rip a chunk out of the wood so you couldn't actually tell any difference in glue strength.

As long as the soundboard is not lumpy in the bridge area, sanding the bridge in place should give you a good fit. I also scrape it slightly concave to compensate for any slight expansion toward convex from water absorption. Heat up the bridge and soundboard, slop glue on the bridge, set it down, and gently rub for a couple seconds until you feel friction with the soundboard wood... at which time it will vacuum in place and be immovable, so it better be in the right spot when it happens The only failure I've had was suspect to begin with (visible glue line at the back of the bridge) and underbraced. I thought about redoing it, but decided to leave it for science, and it did indeed peel off a few years later after the soundboard had deformed quite a bit.

I've had much less luck trying to clamp bridges.

Finger braces and bridge plates can be rub jointed. Radiused X braces, tone bars and back braces must be clamped. Otherwise the plate will spring back flat and overpower the weak glue suction. A couple of little clamps at the ends of the brace could potentially make it work.

I also rub joint my scarf jointed headstocks. Coat the angled surface with thin hide glue and let it dry, sand back flat. Warm it up, apply glue, rub until it grabs and hold by hand for a minute or so until it cools. Then stick 4 cam clamps on it with gentle pressure. They're mainly to prevent the thin corners curling up from moisture expansion (EDIT: also apply water to the outer surfaces before rub jointing to counterbalance moisture expansion from the glue, otherwise the corners may curl immediately when you let go of them to put the clamps on). Too much pressure will shear the joint without a jig to prevent it. You also have to prevent shearing when holding by hand, but that's pretty easy to do. I strength test them with my own body weight, and so far the glue has never failed. The wood did once, due to runout.

The only glue failures I have ever had were to improper clamping so I am not a fan of rubbed joints. It makes sense to me that water will cause wood fibers to expand so when you place a water based glue between two pieces of wood the first thing they want to do is repel eachother as they expand. The idea with HHG is that it has a goot tack and grips the pieces of wood as is dries and shrinks which acts as a 'clamp'. But there is more that one dimension going on here not just push and pull but up and down and so on.

If you clamp the two pieces together then they are stabilized in a perfect position as the glue cures making for a better bond.

Obviously luthiers have been successful doing this for centuries now and in general it may be 'good enough' but when you think of what is happening on a macroscopic level it seems to me that clamping makes a better joint.

I use rub joints for joining plates of fiddles and arch top guitars, with no problems. In my experience it works better than clamping those joints.

As far as I can tell, the purpose of clamps is simply to squeeze out any excess glue, since, in general, a thin glue line (within reason) will be stronger. Rubbing works just as well for this as clamping if the parts fit properly, and you don't keep rubbing after the glue gels, of course.

For what is worth I looked back in my Cumpiano & Natelson book and they show the tentallones method for kerfing they describe basically a rub joint with white glue.

I've used a rub joint on an arch top with the old LMI white glue 20 years ago and as far as I know it's still making music.

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Jim Watts
http://jameswattsguitars.com

Curious if you don’t mind me asking what part of the guitar did you perform a white glue rub joint on?

I basically use a rubbed joint and use tape to keep them even clamping too hard will make a joint weaker.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I made 3 archtop f5 mandolins, all with rub joints. That was 20 years ago and those joint are still going strong today. I use tape only on my guitar top and back. It's hard to find the seam on the top. I may be the slowest guitar builder in the world but I can join two boards really well. I've got that.

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Hutch

Get the heck off the couch and go build a guitar!!!!

The top wedges.

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Jim Watts
http://jameswattsguitars.com